If you don't want to waste resources and run a separate service, you can do a very similar thing with just iptables. Look for the TARPIT target.
> Captures and holds incoming TCP connections using no local per-connection resources. Connections are accepted, but immediately switched to the persist state (0 byte window), in which the remote side stops sending data and asks to continue every 60-240 seconds. Attempts to close the connection are ignored, forcing the remote side to time out the connection in 12-24 minutes.
I'm guessing this may not work, since OP's app sends every 10 seconds and seems to imply that there is some timeout associated with receiving data from the server, but not necessarily a timeout associated with receiving the correct 'SSH-' string needed to move on.
> Captures and holds incoming TCP connections using no local per-connection resources. Connections are accepted, but immediately switched to the persist state (0 byte window), in which the remote side stops sending data and asks to continue every 60-240 seconds. Attempts to close the connection are ignored, forcing the remote side to time out the connection in 12-24 minutes.